Polyether carboxylic acids of the formula RO--(C.sub.2 H.sub.4 O).sub.x CH.sub.2 COOH, wherein R represents a hydrophobic, aliphatic or aliphatic-aromatic residue and x is a number having an average value of about 0.5-10, as well as their alkali metal, alkaline earth metal and quaternary ammonium salts are known surface active compounds which have become of importance in many fields during the last decennia.
In practice such compounds are prepared according to the principles of U.S. Pat. No. 2,623,900, the contents of which are incorporated herein by reference. According to this patent an ethoxylated product of the formula RO--(C.sub.2 H.sub.4 O).sub.x H is reacted in an alkaline medium with an aklaki metal salt of a halo-acetic acid, i.e. with a compound Hal--CH.sub.2 COOM, wherein Hal is a halogen atom and M an aklaki metal. Normally, the salt is a sodium salt, so that the obtained mixture besides the desired final product and unreacted starting product (which is also somewhat surface active and accordingly does not interfere), contains also sodium chloride, which per se is often used as thickening agent for liquid detergents and the like, and accordingly either is useful or in the worst case still is not damaging. In large scale commercial operations, accordingly, it would be desirable, if the so obtained crude reaction mixture could be sold as final product without a complicated further processing, i.e. at low expenses. However, up till now this was not possible, because the obtained mixture is extremely viscous to pasty to almost solid. Of course, the consistency of the obtained product depends somewhat on the nature of the starting materials and the reaction conditions, but this consistency is always such that at room temperature or even at slightly elevated temperatures the product is difficult to handle.
This complication also appears from the examples of U.S. Pat. No. 2,623,900. These examples all describe laboratory experiments and for a part pure compounds are prepared therein, but in examples 4, 6 and 7 technical grade products are used as starting products. As appears from these examples, the direct product of the reaction is always a highly viscous liquid or a paste. In examples 4 and 7 this product is simply dissolved in water. In large scale operations this would mean that an aqueous solution of the crude product would have to be shipped and sold, which of course is not particularly agreeable from an economical standpoint. According to example 6 of the U.S. patent another solution for the problem is chosen, i.e. the obtained mixture is first treated with sulphuric acid, in order to neutralize the excess of sodium hydroxide. Thereby a clear, wax-like mass is obtained which is then spray-dried. However, even in the laboratory this is not a generally valid solution for the problem, because spray-drying is only possible in specific cases. Thus, in the above mentioned example it concerned a product obtained from an adduct of technical grade cetylalcohol with two oxyethylene units. However, most of the crude reaction products in this class are of such a consistency that spray-drying to obtain a really dry product is not feasible, at least at an acceptable price. Moreover, spray-drying has the disadvantage that a relatively expensive treatment is used for a crude product which after that still remains a crude product.
Therefore in the actual practice of large scale operations one usually works in such a way that the crude reaction product is reacted with an excess of acid, usually sulphuric acid, in order to liberate the free polyether carboxylic acid, as is also described in examples 1 and 3 of the above mentioned U.S. patent. Therein diluted sulphuric acid is used and in this way the desired acid is obtained as an oil layer which can be separated from the aqueous layer. Usually, the so obtained acid is then neutralized again, in order to obtain the desired salt, which is then sold either as such or in the form of an aqueous solution. Although in this way a certain purification is attained, this process also removes the originally obtained sodium chloride which is useful for many uses of the product and does not interfere with other uses. Moreover, first an excess of diluted sulphuric acid and then again a base is added and even if this base is a cheap sodium hydroxide solution, this still means a waste of chemicals. When then finally a solution of the product is shipped, this again means a waste, because also a large amount of water is shipped.
Accordingly, it would be desirable to have available a cheap and simple process which makes it possible to convert the obtained high viscosity crude reaction mixture to a pumpable product which can be sold as such.